1. Field of the Invention
The present invention relates to metallurgical practice, and more particularly to a method and apparatus for producing a non-split metal workpiece formed as a cast hollow billet with a bottom part.
The invention can find most utility in the production of shaped castings to be employed in heavy machine-building industry, as well as in the production of thick-wall pipes, vessels, fittings, etc.
2. Description of the Prior Art
The problem of producing profile billets of practically any shape has been long solved in metallurgy by means of conventional casting techniques. However, electroslag metallurgy attracts great interest of those skilled in the art, since it ensures high quality of metal being thereby produced, and makes it possible to utilize this process for the manufacture of special-purpose articles.
Until recently the problem in question has found but partial solutions.
For example, there is known in the art a method of casting hollow billets formed with a bottom part, comprising the steps of premelting slag, pouring it into a mould of an apparatus for producing cast hollow billets formed with bottom parts, and subsequent electroslag remelting of consumable electrodes in a working space of said apparatus. (cf. "Elektroshlakovoye lityo", NIIMASH Review, series IV, Moscow, 1974, pp. 36-38, FIG. 22.delta.). This method starts with forming the bottom part and subsequently the walls of a billet.
An apparatus for producing a hollow billet with a bottom part by the above method /ibid./ comprises a mould mounted on a bottom plate, a mandrel mounted for vertical movement in the mould cavity so that a portion of the cavity adjacent the mould walls and a working surface of the bottom plate remains vacant forming a working space, and consumable electrodes positioned within the working space.
The foregoing method producing a cast hollow billet with a bottom part and the apparatus for practicing this method are efficient in casting billets of relatively small diameter and small ratios of this diameter to wall thickness (less than 10:1). With larger values of the diameter to wall thickness ratio, the electrodes will be spaced far away from the central portion of the bottom part to enable normal thermal conditions in this area of the slag pool, which impairs the formation of the billet bottom surface and results in poor quality of the bottom part metal, caused, in particular, by slag particles being entrapped therein.
A non-uniform temperature field created in the process of casting hollow billets according to this method prevents also the production of complex-shaped bottom parts. Moreover, it is impossible to substantially raise the metling rate of the electroslag process and, accordingly, to increase the rate of production of billets.
The design of the foregoing apparatus for producing a cast hollow billet with a bottom part, which contemplates the process to be carried on in a stationary mould confines its application only to making billets of a relatively short length.
Widening the range of the billet lengths by using a conventional movable mould would entail a considerable complication of the apparatus design because of installation of an additional drive which is imperative in this case, for it is advisable to start moving the mandrel prior to moving the mould to avoid blocking of the mandrel by the solidified metal, especially when producing a hollow billet with a shaped bottom part.
In view of the fact that the problem of producing shaped castings by electroslag method has not yet found its complete solution, a combined technological process has been introduced, comprising various methods of producing separate parts intended for ultimate production of a non-split workpiece of complex configuration. For example, there is known in the prior art one of the most advanced methods for the production of non-split workpieces of complex configuration, which comprises mounting of separate ready-made parts of a workpiece in a shaped mould, and subsequent electroslag remelting of consumable electrodes in the same mould to thereby form the remainder part of the said workpiece and to fuse said ready-made parts thereto (cf. U.S. Pat. No. 3,894,574, U.S. Class 164-52).
The prior art method described above makes it possible to produce workpieces of practically any size and shape, having the advantages of billets produced by the electroslag method (ready-made articles can be obtained by any conventional method, inclusive of electroslag remelting of consumable electrodes).
The method referred to above can be regarded as a successful attempt to solve the above-mentioned problem in general, which makes it possible to produce such complex-shaped articles as crankshafts.
However, this method is relatively complicated in that it requires the supply of ready-made parts for the article to be produced, which involves substantial expenses for the manufacture of such articles. This being the reason for the development of a simple and efficient method for producing shaped billets required for the manufacture of articles less complex in shape than those mentioned above.